Commonly Owned U.S. Pat. Nos. 7,339,531, awarded Mar. 4, 2008 entitled “Multi Frequency Magnetic Dipole Antenna Structures and Method of Reusing the Volume of an Antenna”; 6,943,730 awarded Sep. 13, 2005 entitled “Low-Profile Multi-Frequency, Multi-Band, Capacitively Loaded Magnetic Dipole Antenna”; 6,919,857 awarded Jul. 19, 2005 entitled “Differential Mode Capacitively Loaded Magnetic Dipole Antenna”; 6,900,773 awarded May 31, 2005 entitled “Active Configurable Capacitively Loaded Magnetic Dipole”; 6,859,175 awarded Feb. 22, 2005 entitled “Multiple Frequency Antennas With Reduced Space and Relative Assembly”; 6,744,410 awarded Jun. 1, 2004 entitled “Multi-Band, Low Profile, Capacitively Loaded antennas With Integrated Filters”; and 6,323,810 awarded Nov. 27, 2001 entitled “Multimode Grounded Finger Patch Antenna; and commonly owned co-pending U.S. patent application Ser. No. 11/847,207, filed Aug. 20, 2007, entitled “Antenna With Active Elements,”; and commonly owned co-pending U.S. patent application Ser. No. 12/059,346, filed Mar. 31, 2008, entitled “Multilayer Isolated Magnetic Dipole Antenna,” describe various embodiments of an Isolated Magnetic Dipole (IMD) antenna, their entire contents are hereby incorporated by reference.
The IMD antenna, as illustrated in FIGS. 1a-1b, may comprise a first portion 1, a second portion 2 and a connecting portion 3 therebetween, the first portion and second portion being separated by a gap, wherein the first portion, second portion and connecting portion are substantially disposed within a common plane, and wherein the first portion and second portion are substantially parallel with respect to one another. The geometry of the IMD antenna provides a planar inductive loop 4, and the gap between the first and second portions of the IMD antenna further provides a capacitive loading of the inductive loop, thereby creating a magnetic dipole mode. A feed connects the antenna to a circuit board. In the various embodiments of IMD antennas referenced above, a single resonance IMD antenna can be provided as illustrated in FIG. 1a. Alternatively, a dual resonance IMD antenna can be provided as illustrated in FIG. 1b, wherein the dual resonance antenna comprises a first radiating portion and a second radiating portion, as well as a feed for connecting the antenna to ground.
The magnetic dipole mode of the IMD antenna provides a single or dual resonance and forms an antenna that is efficient and well isolated from the surrounding structure. The dual resonance frequency response can be impedance matched to provide quad or penta-band coverage, allowing for reception, for example, over the 850 GSM, EGSM, DCS, PCS, and WCDMA bands for cellular use. This is, in effect, a self resonant structure that is de-coupled from the local environment. This antenna typically has a single feed for connection of the antenna to the transceiver.
As additional frequency bands are required in the wireless device, tradeoffs are made in terms of matching the single feed antenna structure to a transceiver containing multiple power amplifiers (PA) and receivers. The single feed IMD structure, as described by the prior art, designed to contain two or more resonances that are optimized to provide a radiating structure to service low band (850 GSM and EGSM bands in a handset for example) and high band (DCS, PCS, UMTS) frequency requirements, cannot be optimized for such effects as de-tuning due to the user's head or hand as these effects vary greatly as a function of frequency. Another limitation of the prior art IMD structures includes the difference in transmit power required for GSM and CDMA systems. If active components are integrated into the antenna structure for dynamic tuning, high power components are required in the single feed antenna even when CDMA is operating.
The antenna can be optimized if two or more feed connections can be designed into the single, common antenna structure. This will allow for optimization of the antenna for two or more sets of PAs. An alternate strategy can be provided, where low power CDMA bands are implemented on one feed connection, while higher power GSM bands can be implemented on the second feed connection. This will allow for a combination of low and high power active components to be used on the same antenna structure to dynamically tune or adjust the frequency response of the antenna.
Accordingly, there is a need in the art for an antenna optimized for use with two or more power amplifiers or receivers. There is further a need for an optimized antenna having dual feeds for implementing low power CDMA bands in addition to high power GSM bands. There is also a continuing need for antennas optimized for operation over multiple bands, and designed to function in the presence of interferences associated with the human body. Finally, there remains a need in the art for an antenna system capable of operation over multiple bands, where the antenna is optimized for volume, loss, and cost of manufacture.